Carbon dioxide (CO2) is emitted from common combustion systems and contributes to air pollution. In order to preserve the environment and reduce the emissions of CO2, one approach is to capture and sequester CO2 during industrial processes, before the gas is released into the atmosphere.
The most common commercial technology for capturing CO2 is an amine-based absorption system. However, amine-based systems are limited to relatively small scale (102 ton/day) and low temperature use (between about 49° C. and 140° C.). One approach for overcoming the limitations of amine-based systems is the use of calcium oxide (CaO) inorganic sorbents. However, conventional CaO sorbents have limitations, as well. The performance of conventional CaO sorbents decays with each carbonation/decarbonation cycle. Conventional CaO sorbents sinter at temperatures at or above about 530° C., which also adversely affects the surface area of the sorbent and its CO2-capturing properties. Further, the presence of water vapor in flue gas also reduces the performance of conventional CaO sorbents. Accordingly, a need exists to develop improved CaO sorbents which exhibit high durability under extreme conditions including high temperature and the presence of water vapor.
Along with scale and temperature limitations, conventional CaO sorbents are also susceptible to sulfation by sulfur gases. Carbon dioxide (CO2) and sulfur gases (SO2 and, to a lesser degree, SO3) are emitted together in many common combustion systems. Sulfur gas contaminants adversely affect the performance of CaO-based sorbents, due to reaction competition between carbonation and sulfation. Further, while the carbonation reaction is generally reversible in traditional CaO sorbents, the sulfation reaction is not reversible and accounts for permanent residual weight gain across multiple carbonation/regeneration cycles. Accordingly, a need exists to develop improved CaO sorbents which maintain CO2-capturing properties in the presence of sulfate gas.